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Urease Is Not Essential for Ureide Degradation in Soybean
N. E. Stebbins1, J. C. Polacco
1Department of Biochemistry and Interdisciplinary Plant Group, University of Missouri-Columbia, Columbia, Missouri 65211.
Plant Physiology
|September 1, 1995
Summary
Soybean plants do not significantly convert ureides to urea. Urease-negative soybeans showed minimal urea accumulation from ureides, indicating ureides are poor urea precursors.
Area of Science:
- Plant Physiology
- Biochemistry
- Nitrogen Metabolism
Background:
- Soybean plants utilize nitrogen compounds like ureides and amino acids.
- Urease is an enzyme that hydrolyzes urea.
Purpose of the Study:
- To investigate the extent to which soybean plants catabolize ureides to urea.
- To determine if ureides are significant precursors of urea in soybeans.
Main Methods:
- Utilized urease-negative soybean mutants (Glycine max L. [Merrill]) grown on different nitrogen sources (N2 fixation vs. NH4NO3).
- Analyzed nitrogen content, urea accumulation, and growth in callus cultures with urease-negative and urease-positive cells.
- Employed allopurinol to inhibit ureide formation and traced 14C-labeled compounds (allantoate and arginine) to assess urea conversion.
Main Results:
- Urease-negative plants showed equal seed nitrogen yield regardless of nitrogen source, despite higher leaf urea accumulation in N2-fixing plants.
- Growth reduction in urease-negative callus was greater on arginine than allantoin, with significantly higher urea accumulation from arginine.
- Inhibition of ureide formation did not alter urea levels, and minimal conversion of labeled allantoate to urea was observed, contrasting with significant conversion of arginine to urea.
Conclusions:
- Soybean plants do not catabolize ureides to urea to a physiologically significant extent.
- Ureides are poor precursors of urea in soybean seedlings.
- Arginine is a more significant precursor of urea than ureides in soybean metabolism.